Synchronized mirrored data in a data storage device

ABSTRACT

A data storage device mirrors data on a data storage medium. The multiple instances of data are synchronized in order to optimize performance of the reading and writing, and the integrity of the data. Preferably, a data storage device is allowed to defer writing multiple copies of data until a more advantageous time.

RELATED APPLICATION

This present application is a divisional of and claims priority of U.S.patent application Ser. No. 10/185,063, filed Jun. 28, 2002, now U.S.Pat No. 6,996,668 which claims the benefit of U.S. ProvisionalApplication Ser. No. 60/310,368 filed Aug. 6, 2001, both of which arehereby incorporated by reference in their entirety.

This application is related to U.S. Pat. No. 6,295,577 issued Sep. 25,2001, entitled “Disc storage system having a non-volatile cache to storewrite data in the event of a power failure.”

FIELD OF THE INVENTION

This invention relates generally to data storage devices, and moreparticularly to data mirroring in data storage devices.

BACKGROUND OF THE INVENTION

In order to increase fault tolerance in a group of data storage devices,data mirroring is often implemented. Previously, data mirroring has beenimplemented in redundant array of inexpensive discs (RAID). Datamirroring may be implemented in RAID devices by writing duplicateinstances of data to each of two or more disc drives in the RAID device.Conventional RAID mirroring schemes use controlling technology outsidethe disc drive to manage the duplicated data, such as in a RAIDcontroller. The RAID controller, either in the form of software orhardware, manages which instance of data to read. The data has to bewritten at least twice to synchronize the mirrored data every time thereis a write request. This can cause a performance problem because thenumber of write requests has increased and correspondingly the time tocomplete them has increased.

On the other hand, data mirroring has also been performed in single discdrives. Data mirroring in a single drive poses the same problems as datamirroring in a RAID system, as well as additional problems. Forinstance, the average latency of an unqueued read request in anon-mirrored disc drive is one half revolution because the one instanceof data that is read is one-half of a revolution away from the head whenthe read request is initiated. To improve the inherent latency problemsin a disc drive, data mirroring has been incorporated into disc drives.By placing mirrored data on the same disc drive at different angularpositions, the latency problems associated with a read request have beensubstantially lowered. This is accomplished because the multiple copiesof data, usually placed 180 degrees opposed from each other, reduces theaverage latency of a read request to one-quarter of a revolution.However, the benefits of the performance gain for read requests isoffset by the performance loss of the write requests.

The problem is that a write request must either write all copiesimmediately or deal with complications of having different data on thecopies. If all copies are written immediately, then the average latencyof an unqueued write request is three-quarters of a revolution;one-quarter for the first copy to be written and one-half for the secondcopy to be written.

What is needed is a system, method and/or apparatus that manages thereading and writing of mirrored data in a manner that minimizes theperformance degradation during writes, yet provides the ability to readthe most recently written data.

SUMMARY OF THE INVENTION

The above-mentioned shortcomings, disadvantages and problems areaddressed by the present invention, which will be understood by readingand studying the following specification.

In the present invention, the above mentioned problems are solved byallowing a data storage device to defer writing the copies of the datauntil a more advantageous time. One embodiment of the present inventionprovides a method to select the most effective copy to write.Subsequently, the method may defer the writing of the other copies untila more advantageous time. Another embodiment includes a method thatallows a drive to be self-aware as to whether the copies contain thesame data. Subsequently, the method insures that the most recent copy isreturned on a read request. In addition, the present invention also canbe implemented as a data storage device or as a data storage system.

These and various other features as well as advantages whichcharacterize the present invention will be apparent upon reading of thefollowing detailed description and review of the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that provides a system level overview of theoperation of embodiments of the present invention.

FIG. 2 is a flowchart of a method to manage retrieval of data accordingto an embodiment of the invention.

FIG. 3 is a flowchart of a method to manage writing of data according toan embodiment of the invention.

FIG. 4 is a flowchart of a method to manage synchronized mirrored dataaccording to an embodiment of the invention.

FIG. 5 is a flowchart of a method performed by a data storage device,according to an embodiment of the invention.

FIG. 6 is a flowchart of a method to identify an opportune time to flushwrite at least one write sub-request from an OCW list according to anembodiment of the invention.

FIG. 7 is a flowchart of a method to manage synchronized mirrored dataaccording to an embodiment of the invention.

FIG. 8 is a flowchart of a method to add a new entry to an OCW list,according to an embodiment of the invention.

FIG. 9 is a block diagram of an apparatus to manage retrieval of data,according to an embodiment of the invention.

FIG. 10 is a block diagram of an apparatus to manage writing of data,according to an embodiment of the invention.

FIG. 11 illustrates a plan view of a disc drive incorporating apreferred embodiment of the present invention showing the primaryinternal components.

FIG. 12 illustrates a simplified functional block diagram of the discdrive shown in FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

The invention described in this application is useful for all types ofdata storage devices, including hard-disc drives, optical drives (suchas CDROMs), ZIP drives, floppy-disc drives, and many other types of datastorage devices.

Referring now to FIG. 1, a system level overview 100 of the operation ofembodiments of the present invention is shown. Embodiments of theinvention operate in a data storage device, such as a magnetic discdrive 1300 in FIG. 13.

System 100 manages mirrored data 120 and 125 stored on a data storagemedium 110. System 100 also includes a processor 130 that is operablycoupled to the data storage medium 110 through signal lines 140. System100 also includes synchronization means 150 operative on the processor130 to synchronize the mirrored data 120 and 125 on the data storagemedium 110. In some embodiments, synchronizing accounts for, and/or isperformed in reference to various caching techniques, such as caching ina non-volatile medium, caching in a volatile medium, or no caching. Invarying examples of the synchronization means 150, mirrored data 120 and125 is associated with a write command 160 or a read command 170. Insome examples, the system 100 is incorporated in a data storage device,such as a disc drive, and the data storage medium 110 is a recordingmedium, such as a disc assembly. System 100 provides the advantage ofsynchronizing mirrored data within a data storage device.

In general, there are two manners to perform a write command ofsynchronized data; either all mirrored instances of the write data arewritten immediately to the data storage medium, or the instances arewritten at different times and must be managed on the data storagemedium in a manner that maintains the ability to retrieve the mostcurrent instance. The instances are also known as “copies.” A request towrite an instance is referred to as a write sub-request.

Writing all instances immediately is a solution that is easy toimplement, but is generally lacking in performance. In a rotationalstorage device, such as disc drive 1300, when all instances of data arewritten immediately, the average latency of an unqueued writesub-request is three quarters of a revolution; one quarter of arevolution for the first write and one half of a revolution for a secondwrite, where the copies are written 180 degrees opposed to each other.Writing all instances of synchronized mirrored data is a relativelysimple solution to implement in the firmware of the data storage device.However, this approach can cause temporary peaks in the activity of thedisk drive. The temporary peaks in activity are caused by multiple writesub-requests of mirrored data to the data storage medium of the diskdrive that are performed for each singular write command received by thedisk drive.

Furthermore, a read request for synchronized mirrored data is performedgenerally faster than a read request for unsynchronized non-mirroreddata, as discussed below in conjunction with method 200 in FIG. 2.

Managing synchronized mirrored data on a data storage medium in a mannerthat maintains the ability to retrieve a current instance yields betterperformance than conventional systems. In this manner, a first instanceor instance of the mirrored data is written. After the first instance iswritten, all other instances of the mirrored write data are not written,instead the write sub-requests are deferred until a more advantageous oropportune time. Thus, the initial instance of synchronized mirrored datais written in the same amount of time as one instance of unsynchronizednon-mirrored data in conventional solutions. Deferring the writing ofthe other instances until a time when the drive is idle yields asubstantial performance improvement to a conventional data mirroringsystem and also yields no substantial performance degradation incomparison to writing non-mirrored data systems.

However, writing the first instance of synchronized mirrored data andthe other instances of synchronized mirrored data at different timescreates complexity that must be managed. Read requests to a location inwhich instances do not contain the same data must read the most recentdata. Due to the deferring of the writing of an nth instance, the mostrecent data may only reside in one of the locations or in cache. Powerloss, reset conditions, and any other event that destroys volatilememory contents could prevent the deferred instances from ever beingwritten.

FIG. 2 is a flowchart of a method 200 to manage retrieval of data from adata storage device that has mirrored data according to an embodiment ofthe invention. In general, read performance is improved by selecting themost effective instance to read. Method 200 includes receiving 210 aread command associated with mirrored data that is stored on a datastorage medium in the data storage device. Mirrored data usuallyincludes at least one initial instance of data and at least one copy ofthe initial instance of data. Further, method 200 may includedetermining 220 whether the read command is associated with synchronizedor unsynchronized data. Preferably, in some embodiments, thedetermination is made from data obtained from an outstanding-copy-write(OCW) list.

An OCW list is a data structure, such as a table or a queue, thatindicates write sub-requests that have not been performed to a datastorage medium. When a write sub-request is performed, it is removedfrom the OCW list. The OCW list is discussed in further detail below inrelation to write commands. In some embodiments, the determination isbased on an indicator, such as a bit flag.

When the determining 220 indicates that the data is synchronized, steps270, 280, and 290 may be performed. When the determining 220 indicatesthat the data is unsynchronized, the method 200 has two options enablingit to retrieve the most recent data. The first option includessynchronizing 260 the data by completing the writes related to the OCWentries. Once this is done, the method may proceed to inserting 270 theread sub-requests into the scheduling pool. An alternative to option 1,the method 200 may perform option 2. Option 2 includes finding 250 thecopies with the most recent data. This may require breaking the readrequest into pieces because the most recent data may not exist on onecopy. The method 200 may be designed to include only one of the optionsor both of the options.

When the read command does not specify the most recently written data,the read data is synchronized 260. In one embodiment of thesynchronizing 260, the synchronizing includes completing write commandentries in an OCW list associated with the read command. The OCW listmay include read and write commands for instances of mirrored data.Synchronizing 260 the data is the primary distinction between asynchronized read and an unsynchronized read.

Method 200 continues with inserting 270 one or more, or all, readsub-requests into a scheduling pool. In some embodiments, the readrequest received 210 is divided or partitioned into Y sub-requests whereY is the number of synchronized instances. Thereafter, method 200includes scheduling 280 one of the read sub-requests. In someembodiments, the scheduling pool is implemented with a rotationalposition sorting (RPS) queue. Scheduling 280 may includes schedulingsub-requests in reference to predetermined parameters. For example, in adisc drive 1300, the scheduling may be done in reference to a seek timeand latency of the read sub-request. A scheduling algorithm as disclosedin U.S. Pat. No. 5,570,332 may be used to accomplish this.

Method 200 also includes removing 290 remaining sub-requests from thescheduling pool. The remaining sub-requests are the sub-requests thatwere not scheduled 280. Method 200 can enhance the performance of a datastorage device because the method 200 allows the data storage device todetermine the instance that can be read most quickly. In a preferredembodiment of the present invention, method 200 is completely internalto the data storage device, thus a data storage device is much morecapable than a conventional external controller of optimizing mirroredread performance. For example, where the data storage device is a discdrive, the disc drive uses information that is not readily availableexternally to the data storage device, such as the geometry of the discdrive and current position of the read/write head to schedule theoptimal command.

FIG. 3 is a flowchart of a method 300 to manage writing of data on adata storage device that has synchronized mirrored data, according toone embodiment of the invention.

A write command may either write all instances immediately to the datastorage medium or manage instances on the data storage medium havingvarious versions of the data. If all instances are written immediately,then the average latency of an unqueued write command is three quartersof a revolution. This is often not a desirable solution because this isslower than merely performing the first write sub-request.

One solution is to defer the writing of the copies of the data to a moreadvantageous time. If writing copies is performed at a time when thedata storage medium is idle, there is no performance degradation fromwriting the copies. In contrast, writing copies when the data storagemedium is not idle can degrade performance of the data storage device.The most recent data may only reside in some of the instance locationsor cache. Thus, read sub-requests to a location must read the mostrecent data. Power loss, reset conditions, and any other event thatdestroys memory contents could possibly prevent the cached instancesfrom ever being written.

Method 300 includes receiving 310 a write command that specifies whetherthe data requested is associated with mirrored data. Thereafter, method300 includes determining 320 whether the write command is associatedwith enabled or disabled caching. In some embodiments, the determining320 yields an indication that the write command specifies disabledcaching. Subsequently, the writing 330 of one or more instances of thedata may be performed. The writing 330 can include inserting 332 one ormore write sub-requests into a scheduling pool, scheduling 334 one ormore of the write sub-requests, removing 336 remaining sub-requests fromthe scheduling pool, transferring 338 data associated with the writecommand from host to the recording media, and adding 339 remaining writesub-requests to an OCW list. To enable the OCW list to be accurate inthe event of a power loss or similar condition, once the transferring338 has started, the adding 339 remaining write sub-requests must becompleted. Thus, functions 338 and 339 must be done in an atomic,indivisible manner. In other words, if transferring 338 is started,adding 339 must be guaranteed to complete successfully.

When the write command specifies enabled caching, a caching typedetermination 327 as to whether or not the caching is in a volatilemedium or in a non-volatile medium. When volatile caching is used, amethod 340 is performed that synchronizes the instances of the datarelated to the write request.

Synchronization of data is performed by transferring 341 data associatedwith the write command to a volatile cache and transmitting anindication of completed status to a host (not shown). Next, determining342 restrictions in reference to an OCW list is completed. Thereafter,all write sub-requests are inserted 344 into a scheduling pool. Writecommands are divided or partitioned into N sub-requests for a datastorage device having N instances. Each sub-request may have its ownrotational positional if the N instances are rotationally staggered.

Next, scheduling 346 is done for at least one of the write sub-requests.A write sub-request may be selected 346 from among the plurality ofwrite sub-requests in accordance with a rotational position-sorting(RPS) algorithm. The RPS algorithm selects the sub-request that isassociated with the instance of data that will yield predeterminedthroughput and/or response time characteristics. At least two writesub-requests are scheduled when the determination of OCW restrictionsindicates that adding entries for the sub-requests will cause OCW listentries to logically overlap with one another.

Method 340 also includes removing 348 remaining sub-requests from thescheduling pool. Preferably, the remaining sub-requests that are removed348 were not scheduled 346. After the remaining sub-requests are removed348, transferring 347 data associated with the write command from hostto the recording media is completed. Finally, adding 349 the remainingwrite sub-requests to the OCW list is performed. In some embodiments,write sub-requests that were not added to the OCW list, because ofrestrictions in the OCW list that no longer exist, are added to the OCWlist. In some embodiments, some of the write sub-requests are not addedto the OCW list in order to ensure integrity of the OCW list. In someembodiments, the write sub-requests may be performed rather than storedin the OCW for later performance. In some embodiments, the remainingwrite sub-requests' data may also be saved in the cache in addition tobeing added to an OCW list. To enable the OCW list to be accurate in theevent of a power loss or similar condition, once the transferring 347has started, the adding 349 remaining write sub-requests must becompleted. Thus, functions 347 and 349 must be done in an atomic,indivisible manner. In other words, if transferring 347 is started,adding 349 must be guaranteed to complete successfully.

In some embodiments, when the determining 327 yields an indication thatthe write command is associated with nonvolatile caching, method 350 isaccomplished. Preferably, method 350 includes transferring 351 dataassociated with the write command to a nonvolatile cache. Next, method350 includes inserting 354 an entry into the OCW list that does notspecify an instance; rather, a pointer to data in a cache is included.This type of OCW list entry designates that all copies of the data needto be written. To enable the OCW list to be accurate in the event of apower loss or similar condition, once the transferring 351 has started,the inserting 354 the all copies designated write sub-request must becompleted. Thus, functions 351 and 354 must be done in an atomic,indivisible manner. In other words, if transferring 351 is started,inserting 354 must be guaranteed to complete successfully.

Next, determining 352 restrictions in reference to an OCW list may becompleted. In some embodiments, some of the write sub-requests are notadded to the OCW list in order to ensure integrity of the OCW list. Alsoin some embodiments, the write sub-requests may be performed rather thanstored in the OCW for later performance. Specifically, if adding to theOCW list is not possible without creating overlapping LBA ranges fordifferent instances, the corresponding copies can be synchronized byflushing write sub-requests from the OCW list prior to writing any newdata. Thereafter, method 350 includes inserting 356 all possible writesub-requests into a scheduling pool. Some write sub-requests may not beadded to the OCW list to ensure OCW list integrity; therefore, thesewrite sub-requests must be written to the storage medium.

Subsequently, method 350 includes scheduling 357 at least one of thewrite sub-requests. The write sub-request may be selected from among theplurality of write sub-requests in accordance with a rotationalposition-sorting (RPS) algorithm. The RPS algorithm may select thesub-request that is associated with the instance of data that will yieldpredetermined throughput and/or response time characteristics. At leasttwo write sub-requests are scheduled when the determination of OCWrestrictions indicates that adding entries for the sub-requests willcause OCW list entries to logically overlap with one another.

Method 350 also includes removing 358 remaining sub-requests from thescheduling pool. The remaining write sub-requests are writes that werenot scheduled. The remaining sub-requests may include all of thecorresponding sub-requests that would have been indicated due to the allcopies designation, minus the write sub-request corresponding to thecopy that was written. After the remaining sub-requests are removed 358,transferring 360 data associated with the write command from host to therecording media is completed.

To enable the OCW list to be accurate in the event of a power loss orsimilar condition, once the transferring 360 has started, the adding 359remaining write sub-requests must be completed. Thus, functions 360 and359 must be done in an atomic, indivisible manner. In other words, iftransferring 360 is started, adding 359 must be guaranteed to completesuccessfully.

Finally, method 350 includes removing 359 write sub-requests for thewrite command from the OCW list after the write sub-requests areperformed. The removing 359 may include removing the OCW list entry withthe data pointer that designates all copies need to be written; thenadding all write sub-requests corresponding to unwritten copies to theOCW list. Remaining OCW entries for the original all copies designatedentry no longer need to maintain a cache data pointer.

All write commands of synchronized data involve the use of an OCW listthat represents write sub-requests to the data storage medium that havenot been performed. The OCW list includes one or more entries. In oneembodiment, each entry includes a representation of a logical blockaddress and a representation of which instance of the write request isthe sub-request. For example, an entry may represent the first writesub-request of two write sub-requests that were generated from a writerequest. Each entry may also include a representation of the length ofthe write-data associated with the sub-request, such as the number ofbytes of data of the write sub-request. Further, each entry may alsoinclude a representation of a location of the write-data, such as cache,or nonvolatile cache.

In method 300, ranges of logical block addresses (LBAs) of the OCW listentries are not allowed to logically overlap with one another. Whenadding to the OCW list, entries can be merged to avoid logicallyoverlapping entries. If all write sub-requests can be added to the OCWlist without creating overlapping entries then there may be norestrictions. If only some of the write sub-requests can be added, thenonly non-overlapping write sub-requests are inserted into the OCW list.Allowing only non-overlapping write sub-requests requires restrictingthe scheduling of overlapping instance write(s). If none of the writesub-requests can be added to the OCW list while maintaining nooverlapping entries, then write sub-requests must be flushed from theOCW list to allow entries to be added to the OWC list.

FIG. 4 is a flowchart of a method 400 to manage synchronized mirroreddata in a data storage device according to an embodiment of theinvention. Method 400 may be used when there is a power loss conditionor other condition that destroys the OCW resident memory. Method 400includes copying 410 the OCW list to nonvolatile memory. Whether or notthe OCW list is copied may depend on if the OCW list is not present inthe nonvolatile memory.

Method 400 also includes copying 420 corresponding instance data tononvolatile memory, if nonvolatile write caching is supported. In someembodiments, the copying 420 is performed using back electromotive force(EMF) generated by a rotating member, such as a disc assembly, of thedata storage device. Method 400 enables a data storage device to protectOCW list entries, thus allowing for data synchronization to be completedat a later time.

FIG. 5 is a flowchart of a method 500 to manage synchronized mirroreddata in a data storage device, in which a valid OCW list is present innon-volatile memory. Method 500 may be used in a power-up condition orfor any other condition that requires the OCW list to be restored intooperating memory. Method 500 includes restoring 510 the OCW list tooperating memory and flushing 520 writes from the OCW list duringopportune times. In some embodiments, the restoring 510 does not need tohappen if the OCW list is run-time maintained in nonvolatile memory.

FIG. 6 is a flowchart of a method 1800 to identify an opportune time toflush at least one write sub-request from an OCW list, according to oneembodiment of the invention. An opportune time may be identified in oneof many ways, such as determining 610 that the data storage device isidle. Another opportune time may be identified by determining 620 thatperforming a write to the data storage device from the OCW list willhave an effect on the performance of other functions of the data storagedevice. Usually, a predetermined threshold will be set to monitor theperformance effect of the write to the data storage device. Other waysto determine opportune time to flush write from an OCW list includedetermining 630 that data is being read, with frequency that is at leasta predetermined threshold, from an unsynchronized location of the datastorage device. Still further, an opportune time may be identified bydetermining 640 that the quantity of entries in the OCW list is at leastequal to a predetermined quantity.

FIG. 7 is a flowchart of a method 700 to manage synchronized mirroreddata in a data storage device, according to an embodiment of theinvention. Method 700 may be used to initialize a data storage devicehaving an invalid OCW list in nonvolatile memory. Method 7 may be usedas an alternative to methods 400 and 500 when there is a power losscondition or when recovering from a corrupted OCW list. Method 700includes writing 710 a timestamp to the storage media for every sectorthat is written, determining 720 the most recent data, and, if the datais not synchronized, writing 730 the most recent data to the othercopies. In some embodiments, the determining includes synchronizing databy scanning every copy of every sector to determine the most recentdata.

FIG. 8 illustrates a method 800 to add a new entry to an OCW list,according to an embodiment of the invention. Method 800 includesdetermining 810 whether or not an address associated with the new entryis sequential, overlapping or close to an address associated with anexisting entry in the OCW list. If the address associated with the newentry is sequential, overlapping or close to an address associated withan existing entry in the outstanding-copy-write list, the new entry maybe merged 820 with the existing entry in the OCW list.

A determination 830 is made if an unused entry exists in the OCW list.If an unused entry exists, a new entry is created 840 in the OCW list.If an unused entry does not exist in the OCW list the new entry ismerged 850 with an existing entry. Additionally, method 800 may alsoinclude logically removing 870 any older entries that overlap with theaddress range of the new entry. Method 800 may include merging 860 thenew entry with an existing entry that has the closest LBA range.

FIG. 9 is a block diagram of an apparatus 900 to manage retrieval ofdata from a data storage device that has mirrored data, according to anembodiment of the invention. Apparatus 900 includes a receiver 902 of aread request 909. The read request 909 may identify data to be read. Theread request 909 may be received from a source other than the datastorage device, such as a host computer.

The read request 909 may be associated with mirrored data 920. Themirrored data 920 is stored on a data storage medium 930 in the datastorage device. The mirrored data 920 includes an initial instance ofdata 923, and one or more subsequent instances 926 that aresubstantially duplicates of the initial instance of the data 923.

Apparatus 900 also includes a synchronization determiner 925 for whetherthe read request 909 is associated with synchronized or unsynchronizeddata. In some embodiments, the determination is performed from dataobtained from an OCW list 946. The OCW list 946 may be stored on thestorage medium 930. The result (not shown) of the determination may bestored as a bit flag (not shown).

When the synchronization determiner 925 indicates that the data isunsynchronized, control is passed to a synchronizer 944. In oneembodiment of the synchronizer 944, the synchronizer 944 completes writerequest entries 948 in an OCW list 946 that are associated with theunsynchronized read request 942.

Apparatus 900 includes an inserter 950 of all read sub-requests 951 intoa scheduling pool 956. In one embodiment, each read request 909, isdivided or partitioned into N sub-requests for a drive with N instances.For example, when the data is divided into two identical mirroredinstances, as in the initial instance 923 and the subsequent instance926, the read command is divided or partitioned into two sub-requestssuch as sub-request A 952 and sub-request B 954. Furthermore, eachsub-request has an indication of the unique address that the data isstored on the data storage medium. In some embodiments where the datastorage device is a disc drive, each address includes the rotationalposition of the data because the N instances may be rotationallystaggered on the data storage medium.

Apparatus 900 also includes a scheduler 958 of all of the readsub-requests 951. The scheduler 958 determines the schedule or priorityof the sub-requests 951 in the scheduling pool 956. A sorter 960 in thescheduler 958 uses a rotational position sorting algorithm or analternative algorithm to select the sub-request 962 in the schedulingpool 956 that will yield the best throughput and/or response timecharacteristics that are desired.

Additionally, apparatus 900 includes a remover 964. All sub-requeststhat are not selected for reading are removed from the scheduling pool956 by the remover 964. In some embodiments, the remover 964 removes allassociated sub-requests that remain in the scheduling pool 956 after theselected sub-request 962 is scheduled by the scheduler 958. In someembodiments, the remover 964 removes all associated sub-requests thatremain in the scheduling pool 956 after the selected sub-request 962 isperformed. For example, if the scheduler 958 selected sub-request B fromamong the two sub-requests, sub-request A 952 and sub-request B 954, inscheduling pool 956, after sub-request B 954 is performed, the remover964 removes sub-request A 952 from the scheduling pool 956.

When the determiner 925 indicates that the data is synchronized, controlis passed to the cache 980, which is prompted to send a synchronizedread request 940 to the inserter 950.

As an alternative to apparatus 900, when the synchronization determiner925 yields an indication that the read request 909 specifiesunsynchronized data, the most recent data is read.

In apparatus 900, the data storage device 930 fulfills the read request909 from valid cache data in a cache 980, when the valid cache dataexists, because retrieving data from a cache 980 is typically thefastest manner of retrieving the data. This is done irrespective ofwhether or not the data is synchronized on the data storage medium. Inother words, the read command 909 will be fulfilled or satisfied byvalid cache data in the cache 980 if the data of the read command 909exists, without passing control to the synchronization determiner 925.

Apparatus 900 provides the ability to manage mirrored and/orsynchronized data 920 within the data storage device. Performance ofread operations is improved in apparatus 900 by selecting the mosteffective instance to read, whether the instance that is faster toretrieve is a cached instance or on the data storage medium 930. A datastorage device is much more capable than a conventional externalcontroller of managing and optimizing mirrored read performance. In someembodiments where the data storage device is a disc drive, the discdrive uses information that is not readily available externally to thedata storage device, such as the geometry of the disc drive and currentposition of a read/write head, to schedule the optimal request.

FIG. 10 is a block diagram of an apparatus 1000 to manage writing ofdata on a data storage device that has synchronized mirrored data,according to an embodiment of the invention. Write requests may occur tounsynchronized locations on the media. In this case, the write requestis effectively divided into N sub-requests for a drive with N copies ofthe synchronized data. One of the functions of apparatus 1000 is thatoutstanding writes to the same copy locations may be discarded. Thedrive data storage device may accomplish this by write caching with thisfunctionality. Write caching allows the drive to return status prior towriting a first copy. Alternatively, this functionality may also beincorporated into nonvolatile write caching functionality.

Apparatus 1000 includes a receiver 1010 of a write request 1015. In someembodiments, the write request 1015 is associated with mirrored data.Also included is caching type determiner 1020 for the write request 1015is associated with enabled or disabled caching.

In some embodiments, the determiner 1020 yields an indication that thewrite request 1015 is associated with enabled caching. Where caching isenabled, control is passed to a volatile cache determiner 1030 fordeducing whether the write request 1015 is associated with volatile ornonvolatile caching. Where volatile caching is enabled, control ispassed to a synchronizer 1040 that guarantees and/or ensuressynchronization of data.

Apparatus 1000 includes an inserter 1045 that inserts write sub-requestsinto a scheduling pool 1065. A at least one write sub-request 1051 isgenerated by the inserter 1045 from the write request 1015. Examples ofwrite sub-requests 1051 are write sub-request A 1050 and writesub-request B 1052. One sub-request is generated for each instance ofthe write data 1055 to be written on the data storage medium. Each ofthe plurality of write sub-requests are associated with a unique addresson the data storage medium. In a disc drive, each address may have adifferent rotational positional than each of the other writesub-requests. Writing each of the sub-requests 1051 with differentrotational positions allows subsequent write requests for the mirroreddata to be read quickly by selecting the instance of the data that hasthe closest rotational position. 1

Apparatus 1000 also includes a scheduler 1060 that determines theschedule of the sub-requests in the scheduling pool 1065. The scheduler1060 schedules a selected sub-request 1085. In some embodiments,scheduler 1060 includes a sorter 1062 that uses a rotational positionsorting algorithm or an alternative algorithm to select a sub-request1085. The selected sub-request 1085 is usually selected to yield thebest throughput and/or response time characteristics that are desired.In some embodiments, the desired characteristic is performance, whereinthe sub-request of data that is closest to the rotational position ofthe disc head is selected for writing. The one or more sub-requests thatare not the selected sub-request 1085 are the remaining sub-requests1070.

A writer 1090 is operably coupled to the scheduling pool 1065. Thewriter 1090 performs the selected sub-request 1085 in a data storagemedium 1095. The data 1055 associated with the selected sub-request 1085in the cache 1061 is transferred by the writer 1090 to the data storagemedium 1095.

All sub-requests that are not selected for writing may be removed fromthe scheduling pool 1065. In some embodiments, all associatedsub-requests are removed that remain in the scheduling pool 1065 afterthe selected sub-request 1085 is scheduled by the scheduler 1060. Insome embodiments, all associated sub-requests are removed that remain inthe scheduling pool 1065 after the selected sub-request 1085 isperformed. For example, if the scheduler 1060 selected sub-request Bfrom among the two sub-requests sub-request A 1050 and sub-request B1052 in scheduling pool 1065, after sub-request B 1052 is performed,sub-request A 1050 is removed from the scheduling pool 1065. Thescheduling pool 1065 is operably coupled to the inserter 1045 and thescheduler 1060.

The sub-requests that are not selected are saved in the OCW list 1082 sothat the instances of data in the cache 1060 that are associated withthe remaining sub-requests 1070 can be written to the data storagemedium later.

In some embodiments, the determiner 1030 may yield an indication thatthe write request 1015 is associated with nonvolatile caching. Wherenonvolatile caching is enabled, control passes to a synchronizer 1050that ensures synchronization of data. The adder 1080 inserts adesignated entry that lists all copies in the OCW list.

When the determining 1020 yields an indication, such as a flag, that thewrite request 1015 is associated with disabled caching. Where caching isdisabled, control is passed to inserter 1045.

The OCW list 1082 is a data structure, such as a table, that indicateswrite sub-requests that have not been performed to a data storagemedium. The OCW list includes one or more entries.

The data storage device must always be aware of all remainingoutstanding writes to copies to guarantee that all copies eventuallycontain the same data. All outstanding copy writes are recorded into theOCW (outstanding copy write) list. The necessary information needed tocomplete the outstanding writes is included in the OCW list. Each listentry must include at least the LBA or PBA, length, and copy indicator.A copy indicator referring to the most recent data may also need to besaved if more than two copies exist. If write caching is enabled and nocopies have been written, then the cache memory location of the writedata is also saved. Non-write caching implementations may also save thecache memory location of write data. Non-write caching implementationsmay retain some or all of the write data in cache to improve theperformance of writing other copies. The length of the list is limitedby the amount of volatile memory (if the list is initially stored involatile memory) and nonvolatile memory.

Power loss, hard reset conditions, and events that destroy volatilememory contents require that the drive save information on alloutstanding writes, listed in the OCW list, into a nonvolatile memory.The OCW list must be saved so the drive can synchronize the copies atsome later point in time. Nonvolatile memory can take the form of flashmemory that is programmed upon power loss using back EMF or batteries,battery packed SRAM, or other nonvolatile technologies. For non-volatilecaching, every outstanding internal write is recorded into memory,possibly volatile, at the point status is sent to the host for thewrite. Outstanding writes that are logged into volatile memory aretransferred into nonvolatile memory upon power loss or hard reset or anyother condition that would destroy volatile memory. Corresponding writedata may also have to be transferred to nonvolatile memory ifnonvolatile write caching is enabled and no copies have been written todisc. The drive is still cognizant of all outstanding writes uponrestoration of power or recovery from reset or other condition byreading the OCW list from nonvolatile memory.

FIG. 11 is an exploded view of one embodiment of the present invention,this embodiment showing a disc drive 1100. The disc drive 1100 is oneexample of a data storage device, such as compact disc (CDROM) devices,tape cartridge devices, digital versatile disc (DVD) or digital videodisc (DVD) devices. FIG. 11 provides a top plan view of a disc driveblock data storage device 1100. The disc drive 1100 includes a sealedhousing 1101 formed by a rigid base deck 1102 and a top cover 104 (shownin partial cutaway).

Mechanical components of the disc drive 1100 are supported within thehousing 1101, including a spindle motor 1106 which rotates a number ofrecording discs 1108 at a constant high speed, and an actuator assembly1110 supports a corresponding number of data transducing heads 1112adjacent the discs 1108. The actuator assembly is rotated about anactuator axis through application of current to a coil 1114 of a voicecoil motor (VCM) 1116.

FIG. 12 provides a functional block diagram for the disc drive 1100. Ahardware/firmware based interface circuit 1124 communicates with a hostdevice (such as a personal computer, not shown) and directs overall discdrive operation. The interface circuit 1124 includes a programmablecontroller (processor) 1126 with associated memory 1128, a buffer 1130,an error correction code (ECC) block 1132, a sequencer 1134 and aninput/output (I/O) control block 1136.

The buffer 1130 temporarily stores user data during read and writeoperations, and includes a command queue (CQ) 1131 where multiplepending access operations are temporarily stored pending execution. TheECC block 1132 applies on-the-fly error detection and correction toretrieved data. The sequencer 1134 asserts read and write gates todirect the reading and writing of data. The I/O block 1136 serves as aninterface with the host device.

FIG. 12 further shows the disc drive 1100 to include a read/write (R/W)channel 1138 which encodes and serializes data during write operationsand reconstructs user data from the discs 1108 during read operations. Apreamplifier/driver circuit (preamp) 1140 applies write currents to theheads 1112 and provides pre-amplification of readback signals.

A servo control circuit 1142 uses servo data to provide the appropriatecurrent to the coil 1114 to position the heads 1112 as required. Theservo control circuit 1142 preferably comprises a programmable ARMprocessor 1144 (Advanced Reduced-Instruction-Set-Computer (RISC)Machine). The controller 1126 communicates with the ARM 1144 to move theheads 1112 to the desired locations on the discs 1108 during executionof the various pending access commands in the command queue 1131 inturn.

In summary, a method is provided for receiving 210 a read commandassociated with mirrored data of a data storage medium in a data storagedevice and determining 220 whether the read command is associated withsynchronized or unsynchronized data. Another embodiment may include,inserting 270 at least one read sub-request from the read command into ascheduling pool; scheduling 280 one of the read sub-requests; andremoving 290 remaining sub-requests from the scheduling pool.

Another embodiment is a method comprising the steps of receiving 310 awrite command associated with mirrored data of a data storage medium ina data storage device; and determining 320 whether the write command isassociated with enabled or disabled caching.

Also described is a method to add a new entry to anoutstanding-copy-write list in a data storage device, the methodincluding merging the new entry with the existing entry in theoutstanding-copy-write list, if the address associated with the newentry is sequential, overlapping or close to an address associated withan existing entry in the outstanding-copy-write list; and creating a newentry in the outstanding-copy-write list, if an unused entry exists inthe outstanding-copy-write list and if the address associated with thenew entry is not sequential, overlapping or close to an addressassociated with an existing entry in the outstanding-copy-write list.

Also provided is a method to manage a destructive condition associatedwith an outstanding-copy-write resident list in volatile memory in adata storage device, including copying 410 the outstanding-copy-writelist to nonvolatile memory; and copying 420 corresponding instance datato nonvolatile memory.

Another embodiment includes a method to initialize a data storage devicewith a valid outstanding-copy-write list in nonvolatile memoryassociated with synchronized mirrored data in the data storage device,by restoring 510 the outstanding-copy-write list to operating memory andperforming 520 writes from the outstanding-copy-write list duringopportune times.

In yet another embodiment of the present invention, a method to performentries in an outstanding-copy-write list of a data storage deviceincludes determining 610 that the data storage device is idle. In afurther embodiment, the method includes determining 620 that performinga write to the data storage device from the outstanding-copy-write listwill have an effect on the performance of other functions of the datastorage device that is less than a predetermined threshold. In yetanother embodiment, the method includes determining 630 that data isbeing read with frequency at least equal to a predetermined thresholdfrom an unsynchronized location of the data storage device. The methodmay also include determining 640 that the quantity of entries in theoutstanding-copy-write list is at least equal to a predeterminedquantity.

Another embodiment of the present invention includes a method toinitialize a data storage device having an invalidoutstanding-copy-write list in nonvolatile memory that is associatedwith synchronized mirrored data in the data storage device, includingwriting 710 a timestamp to the recording media for every sector that iswritten; determining 720 the most recent data; and writing 730 the mostrecent data to the other instances, if the data is not synchronized.

A data storage device is also provided including: at least one datastorage medium; and a controller, communicatively coupled to the datastorage medium. The controller including a data structure suitable forrepresenting at least one write sub-request of mirrored data on the datastorage medium that has not been performed to the data storage mediumand a synchronizer of the mirrored data on the data storage medium. Afurther embodiment of the data storage device including a representationof a logical buffer address, if non-volatile caching is being used; arepresentation of the instance of the write request; a representation ofthe length of write-data associated with the sub-request; and arepresentation of a location of the write-data.

It is to be understood that even though numerous characteristics andadvantages of various embodiments of the present invention have been setforth in the foregoing description, together with details of thestructure and function of various embodiments of the invention, thisdisclosure is illustrative only, and changes may be made in detail,especially in matters of structure and arrangement of parts within theprinciples of the present invention to the full extent indicated by thebroad general meaning of the terms in which the appended claims areexpressed. For example, the particular elements may vary depending onthe particular application for the data synchronizing while maintainingsubstantially the same functionality without departing from the scopeand spirit of the present invention. In addition, although the preferredembodiment described herein is directed to a data synchronization methodfor a disc drive, it will be appreciated by those skilled in the artthat the teachings of the present invention can be applied to othersystems, like CD-Rs, CD-RWs, tape or any data storage system, withoutdeparting from the scope and spirit of the present invention.

1. A method comprising the steps of: receiving a command to retrieve data associated with mirrored data of a data storage medium in a data storage device; determining whether the retrieve command is associated with synchronized or unsynchronized data; inserting at least one retrieve sub-request from the retrieve command into a scheduling pool; scheduling one of the retrieve sub-requests; and removing remaining sub-requests from the scheduling pool.
 2. The method of claim 1, and further comprising if the retrieve command is associated with unsynchronized data: synchronizing data.
 3. The method of claim 2, wherein the synchronizing data further comprises the steps of: completing stores of entries in a data structure indicating which store requests have not been completed that are related to the command.
 4. The method of claim 1, if the retrieve command is associated with unsynchronized data: retrieving most recently stored data.
 5. A data storage device comprising: a data storage medium comprising mirrored data; an input for receiving a retrieve command associated with the mirrored data; and a controller, which determines whether the retrieve command is associated with synchronized or unsynchronized data, inserts at least one retrieve sub-request from the retrieve command into a scheduling pool, schedules one of the retrieve sub-requests, and removes remaining sub-requests from the scheduling pool.
 6. The data storage device of claim 5 and further comprising a synchronizer, which synchronizes the data if the retrieve command is associated with unsynchronized data.
 7. The data storage device of claim 6, wherein the controller is further adapted to complete stores of entries in a data structure indicating which store requests have not been completed that are related to the command.
 8. The data storage device of claim 5, the controller is adapted to retrieve most recently stored data if the retrieve command is associated with unsynchronized data. 